#!/usr/bin/perl

# Following is the implementation of simple Class.
package MyClass;

sub new {
   print "MyClass::new called
";
   my $type = shift;            # The package/type name
   my $self = {};               # Reference to empty hash
   return bless $self, $type;   
}

sub DESTROY {
   print "MyClass::DESTROY called
";
}

sub MyMethod {
   print "MyClass::MyMethod called!
";
}


# Following is the implemnetation of Inheritance.
package MySubClass;

@ISA = qw( MyClass );

sub new {
   print "MySubClass::new called
";
   my $type = shift;            # The package/type name
   my $self = MyClass->new;     # Reference to empty hash
   return bless $self, $type;  
}

sub DESTROY {
   print "MySubClass::DESTROY called
";
}

sub MyMethod {
   my $self = shift;
   $self->SUPER::MyMethod();
   print "   MySubClass::MyMethod called!
";
}

# Here is the main program using above classes.
package main;

print "Invoke MyClass method
";

$myObject = MyClass->new();
$myObject->MyMethod();

print "Invoke MySubClass method
";

$myObject2 = MySubClass->new();
$myObject2->MyMethod();

print "Create a scoped object
";
{
   my $myObject2 = MyClass->new();
}
# Destructor is called automatically here

print "Create and undef an object
";
$myObject3 = MyClass->new();
undef $myObject3;

print "Fall off the end of the script...
";
# Remaining destructors are called automatically here

When we execute above program, it produces the following result −

Invoke MyClass method
MyClass::new called
MyClass::MyMethod called!
Invoke MySubClass method
MySubClass::new called
MyClass::new called
MyClass::MyMethod called!
MySubClass::MyMethod called!
Create a scoped object
MyClass::new called
MyClass::DESTROY called
Create and undef an object
MyClass::new called
MyClass::DESTROY called
Fall off the end of the script...
MyClass::DESTROY called
MySubClass::DESTROY called

Perl - Database Access

This chapter teaches you how to access a database inside your Perl script. Starting from Perl 5 has become very easy to write database apppcations using DBI module. DBI stands for Database Independent Interface for Perl, which means DBI provides an abstraction layer between the Perl code and the underlying database, allowing you to switch database implementations really easily.

The DBI is a database access module for the Perl programming language. It provides a set of methods, variables, and conventions that provide a consistent database interface, independent of the actual database being used.

Architecture of a DBI Apppcation

DBI is independent of any database available in backend. You can use DBI whether you are working with Oracle, MySQL or Informix, etc. This is clear from the following architure diagram.

Here DBI is responsible of taking all SQL commands through the API, (i.e., Apppcation Programming Interface) and to dispatch them to the appropriate driver for actual execution. And finally, DBI is responsible of taking results from the driver and giving back it to the calpng scritp.

Notation and Conventions

Throughout this chapter following notations will be used and it is recommended that you should also follow the same convention.

$dsn    Database source name
$dbh    Database handle object
$sth    Statement handle object
$h      Any of the handle types above ($dbh, $sth, or $drh)
$rc     General Return Code  (boolean: true=ok, false=error)
$rv     General Return Value (typically an integer)
@ary    List of values returned from the database.
$rows   Number of rows processed (if available, else -1)
$fh     A filehandle
undef   NULL values are represented by undefined values in Perl
\%attr  Reference to a hash of attribute values passed to methods

Database Connection

Assuming we are going to work with MySQL database. Before connecting to a database make sure of the followings. You can take help of our MySQL tutorial in case you are not aware about how to create database and tables in MySQL database.

You have created a database with a name TESTDB.

You have created a table with a name TEST_TABLE in TESTDB.

This table is having fields FIRST_NAME, LAST_NAME, AGE, SEX and INCOME.

User ID "testuser" and password "test123" are set to access TESTDB.

Perl Module DBI is installed properly on your machine.

You have gone through MySQL tutorial to understand MySQL Basics.

Following is the example of connecting with MySQL database "TESTDB" −

#!/usr/bin/perl

use DBI
use strict;

my $driver = "mysql"; 
my $database = "TESTDB";
my $dsn = "DBI:$driver:database=$database";
my $userid = "testuser";
my $password = "test123";

my $dbh = DBI->connect($dsn, $userid, $password ) or die $DBI::errstr;

If a connection is estabpshed with the datasource then a Database Handle is returned and saved into $dbh for further use otherwise $dbh is set to undef value and $DBI::errstr returns an error string.

INSERT Operation

INSERT operation is required when you want to create some records into a table. Here we are using table TEST_TABLE to create our records. So once our database connection is estabpshed, we are ready to create records into TEST_TABLE. Following is the procedure to create single record into TEST_TABLE. You can create as many as records you pke using the same concept.

Record creation takes the following steps −

Preparing SQL statement with INSERT statement. This will be done using prepare() API.

Executing SQL query to select all the results from the database. This will be done using execute() API.

Releasing Stattement handle. This will be done using finish() API.

If everything goes fine then commit this operation otherwise you can rollback complete transaction. Commit and Rollback are explained in next sections.

my $sth = $dbh->prepare("INSERT INTO TEST_TABLE
                       (FIRST_NAME, LAST_NAME, SEX, AGE, INCOME )
                         values
                       ( john ,  poul ,  M , 30, 13000)");
$sth->execute() or die $DBI::errstr;
$sth->finish();
$dbh->commit or die $DBI::errstr;

Using Bind Values

There may be a case when values to be entered is not given in advance. So you can use bind variables which will take the required values at run time. Perl DBI modules make use of a question mark in place of actual value and then actual values are passed through execute() API at the run time. Following is the example −

my $first_name = "john";
my $last_name = "poul";
my $sex = "M";
my $income = 13000;
my $age = 30;
my $sth = $dbh->prepare("INSERT INTO TEST_TABLE
                        (FIRST_NAME, LAST_NAME, SEX, AGE, INCOME )
                          values
                        (?,?,?,?)");
$sth->execute($first_name,$last_name,$sex, $age, $income) 
          or die $DBI::errstr;
$sth->finish();
$dbh->commit or die $DBI::errstr;

READ Operation

READ Operation on any databasse means to fetch some useful information from the database, i.e., one or more records from one or more tables. So once our database connection is estabpshed, we are ready to make a query into this database. Following is the procedure to query all the records having AGE greater than 20. This will take four steps −

Preparing SQL SELECT query based on required conditions. This will be done using prepare() API.

Executing SQL query to select all the results from the database. This will be done using execute() API.

Fetching all the results one by one and printing those results.This will be done using fetchrow_array() API.

Releasing Stattement handle. This will be done using finish() API.

my $sth = $dbh->prepare("SELECT FIRST_NAME, LAST_NAME
                        FROM TEST_TABLE 
                        WHERE AGE > 20");
$sth->execute() or die $DBI::errstr;
print "Number of rows found :" + $sth->rows;
while (my @row = $sth->fetchrow_array()) {
   my ($first_name, $last_name ) = @row;
   print "First Name = $first_name, Last Name = $last_name
";
}
$sth->finish();

Using Bind Values

There may be a case when condition is not given in advance. So you can use bind variables, which will take the required values at run time. Perl DBI modules makes use of a question mark in place of actual value and then the actual values are passed through execute() API at the run time. Following is the example −

$age = 20;
my $sth = $dbh->prepare("SELECT FIRST_NAME, LAST_NAME
                        FROM TEST_TABLE
                        WHERE AGE > ?");
$sth->execute( $age ) or die $DBI::errstr;
print "Number of rows found :" + $sth->rows;
while (my @row = $sth->fetchrow_array()) {
   my ($first_name, $last_name ) = @row;
   print "First Name = $first_name, Last Name = $last_name
";
}
$sth->finish();

UPDATE Operation

UPDATE Operation on any database means to update one or more records already available in the database tables. Following is the procedure to update all the records having SEX as M . Here we will increase AGE of all the males by one year. This will take three steps −

Preparing SQL query based on required conditions. This will be done using prepare() API.

Executing SQL query to select all the results from the database. This will be done using execute() API.

Releasing Stattement handle. This will be done using finish() API.

If everything goes fine then commit this operation otherwise you can rollback complete transaction. See next section for commit and rollback APIs.

my $sth = $dbh->prepare("UPDATE TEST_TABLE
                        SET   AGE = AGE + 1 
                        WHERE SEX =  M ");
$sth->execute() or die $DBI::errstr;
print "Number of rows updated :" + $sth->rows;
$sth->finish();
$dbh->commit or die $DBI::errstr;

Using Bind Values

There may be a case when condition is not given in advance. So you can use bind variables, which will take required values at run time. Perl DBI modules make use of a question mark in place of actual value and then the actual values are passed through execute() API at the run time. Following is the example −

$sex =  M ;
my $sth = $dbh->prepare("UPDATE TEST_TABLE
                        SET   AGE = AGE + 1
                        WHERE SEX = ?");
$sth->execute( $sex ) or die $DBI::errstr;
print "Number of rows updated :" + $sth->rows;
$sth->finish();
$dbh->commit or die $DBI::errstr;

In some case you would pke to set a value, which is not given in advance so you can use binding value as follows. In this example income of all males will be set to 10000.

$sex =  M ;
$income = 10000;
my $sth = $dbh->prepare("UPDATE TEST_TABLE
                        SET   INCOME = ?
                        WHERE SEX = ?");
$sth->execute( $income,  $sex ) or die $DBI::errstr;
print "Number of rows updated :" + $sth->rows;
$sth->finish();

DELETE Operation

DELETE operation is required when you want to delete some records from your database. Following is the procedure to delete all the records from TEST_TABLE where AGE is equal to 30. This operation will take the following steps.

Preparing SQL query based on required conditions. This will be done using prepare() API.

Executing SQL query to delete required records from the database. This will be done using execute() API.

Releasing Stattement handle. This will be done using finish() API.

If everything goes fine then commit this operation otherwise you can rollback complete transaction.

$age = 30;
my $sth = $dbh->prepare("DELETE FROM TEST_TABLE
                         WHERE AGE = ?");
$sth->execute( $age ) or die $DBI::errstr;
print "Number of rows deleted :" + $sth->rows;
$sth->finish();
$dbh->commit or die $DBI::errstr;

Using do Statement

If you re doing an UPDATE, INSERT, or DELETE there is no data that comes back from the database, so there is a short cut to perform this operation. You can use do statement to execute any of the command as follows.

$dbh->do( DELETE FROM TEST_TABLE WHERE age =30 );

do returns a true value if it succeeded, and a false value if it failed. Actually, if it succeeds it returns the number of affected rows. In the example it would return the number of rows that were actually deleted.

COMMIT Operation

Commit is the operation which gives a green signal to database to finapze the changes and after this operation no change can be reverted to its orignal position.

Here is a simple example to call commit API.

$dbh->commit or die $dbh->errstr;

ROLLBACK Operation

If you are not satisfied with all the changes or you encounter an error in between of any operation , you can revert those changes to use rollback API.

Here is a simple example to call rollback API.

$dbh->rollback or die $dbh->errstr;

Begin Transaction

Many databases support transactions. This means that you can make a whole bunch of queries which would modify the databases, but none of the changes are actually made. Then at the end, you issue the special SQL query COMMIT, and all the changes are made simultaneously. Alternatively, you can issue the query ROLLBACK, in which case all the changes are thrown away and database remains unchanged.

Perl DBI module provided begin_work API, which enables transactions (by turning AutoCommit off) until the next call to commit or rollback. After the next commit or rollback, AutoCommit will automatically be turned on again.

$rc  = $dbh->begin_work  or die $dbh->errstr;

AutoCommit Option

If your transactions are simple, you can save yourself the trouble of having to issue a lot of commits. When you make the connect call, you can specify an AutoCommit option which will perform an automatic commit operation after every successful query. Here s what it looks pke −

my $dbh = DBI->connect($dsn, $userid, $password,
              {AutoCommit => 1}) 
              or die $DBI::errstr;

Here AutoCommit can take value 1 or 0, where 1 means AutoCommit is on and 0 means AutoCommit is off.

Automatic Error Handpng

When you make the connect call, you can specify a RaiseErrors option that handles errors for you automatically. When an error occurs, DBI will abort your program instead of returning a failure code. If all you want is to abort the program on an error, this can be convenient. Here s what it looks pke −

my $dbh = DBI->connect($dsn, $userid, $password,
              {RaiseError => 1})
              or die $DBI::errstr;

Here RaiseError can take value 1 or 0.

Disconnecting Database

To disconnect Database connection, use disconnect API as follows −

$rc = $dbh->disconnect  or warn $dbh->errstr;

The transaction behaviour of the disconnect method is, sadly, undefined. Some database systems (such as Oracle and Ingres) will automatically commit any outstanding changes, but others (such as Informix) will rollback any outstanding changes. Apppcations not using AutoCommit should exppcitly call commit or rollback before calpng disconnect.

Using NULL Values

Undefined values, or undef, are used to indicate NULL values. You can insert and update columns with a NULL value as you would a non-NULL value. These examples insert and update the column age with a NULL value −

$sth = $dbh->prepare(qq {
         INSERT INTO TEST_TABLE (FIRST_NAME, AGE) VALUES (?, ?)
       });
$sth->execute("Joe", undef);

Here qq{} is used to return a quoted string to prepare API. However, care must be taken when trying to use NULL values in a WHERE clause. Consider −

SELECT FIRST_NAME FROM TEST_TABLE WHERE age = ?

Binding an undef (NULL) to the placeholder will not select rows, which have a NULL age! At least for database engines that conform to the SQL standard. Refer to the SQL manual for your database engine or any SQL book for the reasons for this. To exppcitly select NULLs you have to say "WHERE age IS NULL".

A common issue is to have a code fragment handle a value that could be either defined or undef (non-NULL or NULL) at runtime. A simple technique is to prepare the appropriate statement as needed, and substitute the placeholder for non-NULL cases −

$sql_clause = defined $age? "age = ?" : "age IS NULL";
$sth = $dbh->prepare(qq {
         SELECT FIRST_NAME FROM TEST_TABLE WHERE $sql_clause
       });
$sth->execute(defined $age ? $age : ());

Some Other DBI Functions

available_drivers

@ary = DBI->available_drivers;
@ary = DBI->available_drivers($quiet);

Returns a pst of all available drivers by searching for DBD::* modules through the directories in @INC. By default, a warning is given if some drivers are hidden by others of the same name in earper directories. Passing a true value for $quiet will inhibit the warning.

installed_drivers

%drivers = DBI->installed_drivers();

Returns a pst of driver name and driver handle pairs for all drivers installed (loaded) into the current process. The driver name does not include the DBD:: prefix.

data_sources

@ary = DBI->data_sources($driver);

Returns a pst of data sources (databases) available via the named driver. If $driver is empty or undef, then the value of the DBI_DRIVER environment variable is used.

quote

$sql = $dbh->quote($value);
$sql = $dbh->quote($value, $data_type);

Quote a string pteral for use as a pteral value in an SQL statement, by escaping any special characters (such as quotation marks) contained within the string and adding the required type of outer quotation marks.

$sql = sprintf "SELECT foo FROM bar WHERE baz = %s",
                $dbh->quote("Don t");

For most database types, quote would return Don t (including the outer quotation marks). It is vapd for the quote() method to return an SQL expression that evaluates to the desired string. For example −

$quoted = $dbh->quote("one
twothree")

may produce results which will be equivalent to

CONCAT( one , CHAR(12),  two , CHAR(0),  three )

Methods Common to All Handles

err

$rv = $h->err;
or
$rv = $DBI::err
or
$rv = $h->err

Returns the native database engine error code from the last driver method called. The code is typically an integer but you should not assume that. This is equivalent to $DBI::err or $h->err.

errstr

$str = $h->errstr;
or
$str = $DBI::errstr
or
$str = $h->errstr

Returns the native database engine error message from the last DBI method called. This has the same pfespan issues as the "err" method described above. This is equivalent to $DBI::errstr or $h->errstr.

rows

$rv = $h->rows;
or
$rv = $DBI::rows

This returns the number of rows effected by previous SQL statement and equivalent to $DBI::rows.

trace

$h->trace($trace_settings);

DBI sports an extremely useful abipty to generate runtime tracing information of what it s doing, which can be a huge time-saver when trying to track down strange problems in your DBI programs. You can use different values to set trace level. These values varies from 0 to 4. The value 0 means disable trace and 4 means generate complete trace.

Interpolated Statements are Prohibited

It is highly recommended not to use interpolated statements as follows −

while ($first_name = <>) {
   my $sth = $dbh->prepare("SELECT * 
                          FROM TEST_TABLE 
                          WHERE FIRST_NAME =  $first_name ");
   $sth->execute();
   # and so on ...
}

Thus don t use interpolated statement instead use bind value to prepare dynamic SQL statement.

Perl - CGI Programming

What is CGI ?

A Common Gateway Interface, or CGI, is a set of standards that defines how information is exchanged between the web server and a custom script.

The CGI specs are currently maintained by the NCSA and NCSA defines CGI is as follows −

The Common Gateway Interface, or CGI, is a standard for external gateway programs to interface with information servers such as HTTP servers.

The current version is CGI/1.1 and CGI/1.2 is under progress.

Web Browsing

To understand the concept of CGI, lets see what happens when we cpck a hyper pnk available on a web page to browse a particular web page or URL.

Your browser contacts web server using HTTP protocol and demands for the URL, i.e., web page filename.

Web Server will check the URL and will look for the filename requested. If web server finds that file then it sends the file back to the browser without any further execution otherwise sends an error message indicating that you have requested a wrong file.

Web browser takes response from web server and displays either the received file content or an error message in case file is not found.

However, it is possible to set up HTTP server in such a way so that whenever a file in a certain directory is requested that file is not sent back; instead it is executed as a program, and whatever that program outputs as a result, that is sent back for your browser to display. This can be done by using a special functionapty available in the web server and it is called Common Gateway Interface or CGI and such programs which are executed by the server to produce final result, are called CGI scripts. These CGI programs can be a PERL Script, Shell Script, C or C++ program, etc.

CGI Architecture Diagram

Web Server Support and Configuration

Before you proceed with CGI Programming, make sure that your Web Server supports CGI functionapty and it is configured to handle CGI programs. All the CGI programs to be executed by the web server are kept in a pre-configured directory. This directory is called CGI directory and by convention it is named as /cgi-bin. By convention Perl CGI files will have extention as .cgi.

First CGI Program

Here is a simple pnk which is pnked to a CGI script called hello.cgi. This file has been kept in /cgi-bin/ directory and it has the following content. Before running your CGI program, make sure you have change mode of file using chmod 755 hello.cgi UNIX command.

#!/usr/bin/perl

print "Content-type:text/html

";
print  <html> ;
print  <head> ;
print  <title>Hello Word - First CGI Program</title> ;
print  </head> ;
print  <body> ;
print  <h2>Hello Word! This is my first CGI program</h2> ;
print  </body> ;
print  </html> ;

1;

Now if you cpck hello.cgi pnk then request goes to web server who search for hello.cgi in /cgi-bin directory, execute it and whatever result got generated, web server sends that result back to the web browser, which is as follows −

Hello Word! This is my first CGI program

This hello.cgi script is a simple Perl script which is writing its output on STDOUT file, i.e., screen. There is one important and extra feature available which is first pne to be printed Content-type:text/html . This pne is sent back to the browser and specifies the content type to be displayed on the browser screen. Now you must have undertood basic concept of CGI and you can write many comppcated CGI programs using Perl. This script can interact with any other exertnal system also to exchange information such as a database, web services, or any other complex interfaces.

Understanding HTTP Header

The very first pne Content-type:text/html is a part of HTTP header, which is sent to the browser so that browser can understand the incoming content from server side. All the HTTP header will be in the following form −

HTTP Field Name: Field Content

For Example −

Content-type:text/html

There are few other important HTTP headers, which you will use frequently in your CGI Programming.

CGI Environment Variables

All the CGI program will have access to the following environment variables. These variables play an important role while writing any CGI program.

Here is a small CGI program to pst down all the CGI variables supported by your Web server. Cpck this pnk to see the result Get Environment

#!/usr/bin/perl

print "Content-type: text/html

";
print "<font size=+1>Environment</font>
";
foreach (sort keys %ENV) {
   print "<b>$_</b>: $ENV{$_}<br>
";
}

1;

Raise a "File Download" Dialog Box?

Sometime it is desired that you want to give option where a user will cpck a pnk and it will pop up a "File Download" dialogue box to the user instead of displaying actual content. This is very easy and will be achived through HTTP header.

This HTTP header will be different from the header mentioned in previous section. For example, if you want to make a FileName file downloadable from a given pnk then it s syntax will be as follows −

#!/usr/bin/perl

# HTTP Header
print "Content-Type:apppcation/octet-stream; name = "FileName"
";
print "Content-Disposition: attachment; filename = "FileName"

";

# Actual File Content will go hear.
open( FILE, "<FileName" );
while(read(FILE, $buffer, 100) ) {
   print("$buffer");
}

GET and POST Methods

You must have come across many situations when you need to pass some information from your browser to the web server and ultimately to your CGI Program handpng your requests. Most frequently browser uses two methods to pass this information to the web server. These methods are GET Method and POST Method. Let s check them one by one.

Passing Information using GET Method

The GET method sends the encoded user information appended to the page URL itself. The page and the encoded information are separated by the ? character as follows −

http://www.test.com/cgi-bin/hello.cgi?key1=value1&key2=value2

The GET method is the defualt method to pass information from a browser to the web server and it produces a long string that appears in your browser s Location:box. You should never use GET method if you have password or other sensitive information to pass to the server. The GET method has size pmitation: only 1024 characters can be passed in a request string.

This information is passed using QUERY_STRING header and will be accessible in your CGI Program through QUERY_STRING environment variable which you can parse and use in your CGI program.

You can pass information by simply concatenating key and value pairs alongwith any URL or you can use HTML <FORM> tags to pass information using GET method.

Simple URL Example: Get Method

Here is a simple URL which will pass two values to hello_get.cgi program using GET method.

Below is hello_get.cgi script to handle input given by web browser.

#!/usr/bin/perl

local ($buffer, @pairs, $pair, $name, $value, %FORM);
# Read in text
$ENV{ REQUEST_METHOD } =~ tr/a-z/A-Z/;
if ($ENV{ REQUEST_METHOD } eq "GET") {
   $buffer = $ENV{ QUERY_STRING };
}
# Sppt information into name/value pairs
@pairs = sppt(/&/, $buffer);
foreach $pair (@pairs) {
   ($name, $value) = sppt(/=/, $pair);
   $value =~ tr/+/ /;
   $value =~ s/%(..)/pack("C", hex($1))/eg;
   $FORM{$name} = $value;
}
$first_name = $FORM{first_name};
$last_name  = $FORM{last_name};

print "Content-type:text/html

";
print "<html>";
print "<head>";
print "<title>Hello - Second CGI Program</title>";
print "</head>";
print "<body>";
print "<h2>Hello $first_name $last_name - Second CGI Program</h2>";
print "</body>";
print "</html>";

1;

Simple FORM Example: GET Method

Here is a simple example, which passes two values using HTML FORM and submit button. We are going to use the same CGI script hello_get.cgi to handle this input.

<FORM action = "/cgi-bin/hello_get.cgi" method = "GET">
First Name: <input type = "text" name = "first_name">  <br>

Last Name: <input type = "text" name = "last_name">
<input type = "submit" value = "Submit">
</FORM>

Here is the actual output of the above form coding. Now you can enter First and Last Name and then cpck submit button to see the result.

Passing Information using POST Method

A more repable method of passing information to a CGI program is the POST method. This packages the information in exactly the same way as GET methods, but instead of sending it as a text string after a ? in the URL, it sends it as a separate message as a part of HTTP header. Web server provides this message to the CGI script in the form of the standard input.

Below is the modified hello_post.cgi script to handle input given by the web browser. This script will handle GET as well as POST method.

#!/usr/bin/perl

local ($buffer, @pairs, $pair, $name, $value, %FORM);
# Read in text
$ENV{ REQUEST_METHOD } =~ tr/a-z/A-Z/;
if ($ENV{ REQUEST_METHOD } eq "POST") {
   read(STDIN, $buffer, $ENV{ CONTENT_LENGTH });
} else {
   $buffer = $ENV{ QUERY_STRING };
}
# Sppt information into name/value pairs
@pairs = sppt(/&/, $buffer);
foreach $pair (@pairs) {
   ($name, $value) = sppt(/=/, $pair);
   $value =~ tr/+/ /;
   $value =~ s/%(..)/pack("C", hex($1))/eg;
   $FORM{$name} = $value;
}
$first_name = $FORM{first_name};
$last_name  = $FORM{last_name};

print "Content-type:text/html

";
print "<html>";
print "<head>";
print "<title>Hello - Second CGI Program</title>";
print "</head>";
print "<body>";
print "<h2>Hello $first_name $last_name - Second CGI Program</h2>";
print "</body>";
print "</html>";

1;

Let us take again same examle as above, which passes two values using HTML FORM and submit button. We are going to use CGI script hello_post.cgi to handle this input.

<FORM action = "/cgi-bin/hello_post.cgi" method = "POST">
First Name: <input type = "text" name = "first_name">  <br>

Last Name: <input type = "text" name = "last_name">

<input type = "submit" value = "Submit">
</FORM>

Here is the actual output of the above form coding, You enter First and Last Name and then cpck submit button to see the result.

Passing Checkbox Data to CGI Program

Checkboxes are used when more than one option is required to be selected. Here is an example HTML code for a form with two checkboxes.

<form action = "/cgi-bin/checkbox.cgi" method = "POST" target = "_blank">
<input type = "checkbox" name = "maths" value = "on"> Maths
<input type = "checkbox" name = "physics" value = "on"> Physics
<input type = "submit" value = "Select Subject">
</form>

The result of this code is the following form −

Below is checkbox.cgi script to handle input given by web browser for radio button.

#!/usr/bin/perl

local ($buffer, @pairs, $pair, $name, $value, %FORM);
# Read in text
$ENV{ REQUEST_METHOD } =~ tr/a-z/A-Z/;
if ($ENV{ REQUEST_METHOD } eq "POST") {
   read(STDIN, $buffer, $ENV{ CONTENT_LENGTH });
} else {
   $buffer = $ENV{ QUERY_STRING };
}
# Sppt information into name/value pairs
@pairs = sppt(/&/, $buffer);
foreach $pair (@pairs) {
   ($name, $value) = sppt(/=/, $pair);
   $value =~ tr/+/ /;
   $value =~ s/%(..)/pack("C", hex($1))/eg;
   $FORM{$name} = $value;
}
if( $FORM{maths} ) {
   $maths_flag ="ON";
} else {
   $maths_flag ="OFF";
}
if( $FORM{physics} ) {
   $physics_flag ="ON";
} else {
   $physics_flag ="OFF";
}

print "Content-type:text/html

";
print "<html>";
print "<head>";
print "<title>Checkbox - Third CGI Program</title>";
print "</head>";
print "<body>";
print "<h2> CheckBox Maths is : $maths_flag</h2>";
print "<h2> CheckBox Physics is : $physics_flag</h2>";
print "</body>";
print "</html>";

1;

Passing Radio Button Data to CGI Program

Radio Buttons are used when only one option is required to be selected. Here is an example HTML code for a form with two radio button −

<form action = "/cgi-bin/radiobutton.cgi" method = "POST" target = "_blank">
<input type = "radio" name = "subject" value = "maths"> Maths
<input type = "radio" name = "subject" value = "physics"> Physics
<input type = "submit" value = "Select Subject">
</form>

The result of this code is the following form −

Below is radiobutton.cgi script to handle input given by the web browser for radio button.

#!/usr/bin/perl

local ($buffer, @pairs, $pair, $name, $value, %FORM);
# Read in text
$ENV{ REQUEST_METHOD } =~ tr/a-z/A-Z/;
if ($ENV{ REQUEST_METHOD } eq "POST") {
   read(STDIN, $buffer, $ENV{ CONTENT_LENGTH });
} else {
   $buffer = $ENV{ QUERY_STRING };
}
# Sppt information into name/value pairs
@pairs = sppt(/&/, $buffer);
foreach $pair (@pairs) {
   ($name, $value) = sppt(/=/, $pair);
   $value =~ tr/+/ /;
   $value =~ s/%(..)/pack("C", hex($1))/eg;
   $FORM{$name} = $value;
}
$subject = $FORM{subject};

print "Content-type:text/html

";
print "<html>";
print "<head>";
print "<title>Radio - Fourth CGI Program</title>";
print "</head>";
print "<body>";
print "<h2> Selected Subject is $subject</h2>";
print "</body>";
print "</html>";

1;

Passing Text Area Data to CGI Program

A textarea element is used when multipne text has to be passed to the CGI Program. Here is an example HTML code for a form with a TEXTAREA box −

<form action = "/cgi-bin/textarea.cgi" method = "POST" target = "_blank">
<textarea name = "textcontent" cols = 40 rows = 4>
Type your text here...
</textarea>
<input type = "submit" value = "Submit">
</form>

The result of this code is the following form −

Below is the textarea.cgi script to handle input given by the web browser.

#!/usr/bin/perl

local ($buffer, @pairs, $pair, $name, $value, %FORM);
# Read in text
$ENV{ REQUEST_METHOD } =~ tr/a-z/A-Z/;
if ($ENV{ REQUEST_METHOD } eq "POST") {
   read(STDIN, $buffer, $ENV{ CONTENT_LENGTH });
} else {
   $buffer = $ENV{ QUERY_STRING };
}
# Sppt information into name/value pairs
@pairs = sppt(/&/, $buffer);
foreach $pair (@pairs) {
   ($name, $value) = sppt(/=/, $pair);
   $value =~ tr/+/ /;
   $value =~ s/%(..)/pack("C", hex($1))/eg;
   $FORM{$name} = $value;
}
$text_content = $FORM{textcontent};

print "Content-type:text/html

";
print "<html>";
print "<head>";
print "<title>Text Area - Fifth CGI Program</title>";
print "</head>";
print "<body>";
print "<h2> Entered Text Content is $text_content</h2>";
print "</body>";
print "</html>";

1;

Passing Drop Down Box Data to CGI Program

A drop down box is used when we have many options available but only one or two will be selected. Here is example HTML code for a form with one drop down box

<form action = "/cgi-bin/dropdown.cgi" method = "POST" target = "_blank">
<select name = "dropdown">
<option value = "Maths" selected>Maths</option>
<option value = "Physics">Physics</option>
</select>
<input type = "submit" value = "Submit">
</form>

The result of this code is the following form −

Below is the dropdown.cgi script to handle input given by web browser.

#!/usr/bin/perl

local ($buffer, @pairs, $pair, $name, $value, %FORM);
# Read in text
$ENV{ REQUEST_METHOD } =~ tr/a-z/A-Z/;
if ($ENV{ REQUEST_METHOD } eq "POST") {
   read(STDIN, $buffer, $ENV{ CONTENT_LENGTH });
} else {
   $buffer = $ENV{ QUERY_STRING };
}
# Sppt information into name/value pairs
@pairs = sppt(/&/, $buffer);
foreach $pair (@pairs) {
   ($name, $value) = sppt(/=/, $pair);
   $value =~ tr/+/ /;
   $value =~ s/%(..)/pack("C", hex($1))/eg;
   $FORM{$name} = $value;
}
$subject = $FORM{dropdown};

print "Content-type:text/html

";
print "<html>";
print "<head>";
print "<title>Dropdown Box - Sixth CGI Program</title>";
print "</head>";
print "<body>";
print "<h2> Selected Subject is $subject</h2>";
print "</body>";
print "</html>";

1;

Using Cookies in CGI

HTTP protocol is a stateless protocol. But for a commercial website it is required to maintain session information among different pages. For example one user registration ends after transactions which spans through many pages. But how to maintain user s session information across all the web pages?

In many situations, using cookies is the most efficient method of remembering and tracking preferences, purchases, commissions, and other information required for better visitor experience or site statistics.

How It Works

Your server sends some data to the visitor s browser in the form of a cookie. The browser may accept the cookie. If it does, it is stored as a plain text record on the visitor s hard drive. Now, when the visitor arrives at another page on your site, the cookie is available for retrieval. Once retrieved, your server knows/remembers what was stored.

Cookies are a plain text data record of 5 variable-length fields −

Expires − The date the cookie will expire. If this is blank, the cookie will expire when the visitor quits the browser.

Domain − The domain name of your site.

Path − The path to the directory or web page that set the cookie. This may be blank if you want to retrieve the cookie from any directory or page.

Secure − If this field contains the word "secure" then the cookie may only be retrieved with a secure server. If this field is blank, no such restriction exists.

Name = Value − Cookies are set and retrviewed in the form of key and value pairs.

Setting up Cookies

It is very easy to send cookies to browser. These cookies will be sent along with the HTTP Header. Assuming you want to set UserID and Password as cookies. So it will be done as follows −

#!/usr/bin/perl

print "Set-Cookie:UserID = XYZ;
";
print "Set-Cookie:Password = XYZ123;
";
print "Set-Cookie:Expires = Tuesday, 31-Dec-2007 23:12:40 GMT";
";
print "Set-Cookie:Domain = www.tutorialspoint.com;
";
print "Set-Cookie:Path = /perl;
";
print "Content-type:text/html

";
...........Rest of the HTML Content goes here....

Here we used Set-Cookie HTTP header to set cookies. It is optional to set cookies attributes pke Expires, Domain, and Path. It is important to note that cookies are set before sending magic pne "Content-type:text/html .

Retrieving Cookies

It is very easy to retrieve all the set cookies. Cookies are stored in CGI environment variable HTTP_COOKIE and they will have following form.

key1 = value1;key2 = value2;key3 = value3....

Here is an example of how to retrieve cookies.

#!/usr/bin/perl
$rcvd_cookies = $ENV{ HTTP_COOKIE };
@cookies = sppt /;/, $rcvd_cookies;
foreach $cookie ( @cookies ) {
   ($key, $val) = sppt(/=/, $cookie); # sppts on the first =.
   $key =~ s/^s+//;
   $val =~ s/^s+//;
   $key =~ s/s+$//;
   $val =~ s/s+$//;
   if( $key eq "UserID" ) {
      $user_id = $val;
   } elsif($key eq "Password") {
      $password = $val;
   }
}
print "User ID  = $user_id
";
print "Password = $password
";

This will produce the following result, provided above cookies have been set before calpng retrieval cookies script.

User ID = XYZ
Password = XYZ123

CGI Modules and Libraries

You will find many built-in modules over the internet which provides you direct functions to use in your CGI program. Following are the important once.

CGI Module

Berkeley cgi-pb.pl

Perl - Packages and Modules

What are Packages?

The package statement switches the current naming context to a specified namespace (symbol table). Thus −

A package is a collection of code which pves in its own namespace.

A namespace is a named collection of unique variable names (also called a symbol table).

Namespaces prevent variable name colpsions between packages.

Packages enable the construction of modules which, when used, won t clobber variables and functions outside of the modules s own namespace.

The package stays in effect until either another package statement is invoked, or until the end of the current block or file.

You can exppcitly refer to variables within a package using the :: package quapfier.

Following is an example having main and Foo packages in a file. Here special variable __PACKAGE__ has been used to print the package name.

#!/usr/bin/perl

# This is main package
$i = 1; 
print "Package name : " , __PACKAGE__ , " $i
"; 

package Foo;
# This is Foo package
$i = 10; 
print "Package name : " , __PACKAGE__ , " $i
"; 

package main;
# This is again main package
$i = 100; 
print "Package name : " , __PACKAGE__ , " $i
"; 
print "Package name : " , __PACKAGE__ ,  " $Foo::i
"; 

1;

Package name : main 1
Package name : Foo 10
Package name : main 100
Package name : main 10

BEGIN { ... }
END { ... }
BEGIN { ... }
END { ... }

#!/usr/bin/perl

package Foo;
print "Begin and Block Demo
";

BEGIN { 
   print "This is BEGIN Block
" 
}

END { 
   print "This is END Block
" 
}

1;

This is BEGIN Block
Begin and Block Demo
This is END Block

#!/usr/bin/perl

package Foo;
sub bar { 
   print "Hello $_[0]
" 
}

sub blat { 
   print "World $_[0]
" 
}
1;

#!/usr/bin/perl

require Foo;

Foo::bar( "a" );
Foo::blat( "b" );

#!/usr/bin/perl

use Foo;

bar( "a" );
blat( "b" );

require Exporter;
@ISA = qw(Exporter);

package Module;

require Exporter;
@ISA = qw(Exporter);
@EXPORT = qw(bar blat);

sub bar { print "Hello $_[0]
" }
sub blat { print "World $_[0]
" }
sub splat { print "Not $_[0]
" }  # Not exported!

1;

$h2xs -AX -n  ModuleName

$h2xs -AX -n Person

Writing Person/pb/Person.pm
Writing Person/Makefile.PL
Writing Person/README
Writing Person/t/Person.t
Writing Person/Changes
Writing Person/MANIFEST

tar xvfz Person.tar.gz
cd Person
perl Makefile.PL
make
make install

#!/usr/bin/perl

@files = `ls -l`;

foreach $file (@files) {
   print $file;
}

1;

drwxr-xr-x 3 root root 4096 Sep 14 06:46 9-14
drwxr-xr-x 4 root root 4096 Sep 13 07:54 android
-rw-r--r-- 1 root root  574 Sep 17 15:16 index.htm
drwxr-xr-x 3  544  401 4096 Jul  6 16:49 MIME-Lite-3.01
-rw-r--r-- 1 root root   71 Sep 17 15:16 test.pl
drwx------ 2 root root 4096 Sep 17 15:11 vAtrJdy

#!/usr/bin/perl

system( "ls -l")

1;

drwxr-xr-x 3 root root 4096 Sep 14 06:46 9-14
drwxr-xr-x 4 root root 4096 Sep 13 07:54 android
-rw-r--r-- 1 root root  574 Sep 17 15:16 index.htm
drwxr-xr-x 3  544  401 4096 Jul  6 16:49 MIME-Lite-3.01
-rw-r--r-- 1 root root   71 Sep 17 15:16 test.pl
drwx------ 2 root root 4096 Sep 17 15:11 vAtrJdy

#!/usr/bin/perl

$PATH = "I am Perl Variable";

system( echo $PATH );  # Treats $PATH as shell variable
system("echo $PATH");  # Treats $PATH as Perl variable
system("echo $PATH"); # Escaping $ works.

1;

/usr/local/bin:/bin:/usr/bin:/usr/local/sbin:/usr/sbin:/sbin
I am Perl Variable
/usr/local/bin:/bin:/usr/bin:/usr/local/sbin:/usr/sbin:/sbin

#!/usr/bin/perl

if(!defined($pid = fork())) {
   # fork returned undef, so unsuccessful
   die "Cannot fork a child: $!";
} elsif ($pid == 0) {
   print "Printed by child process
";
   exec("date") || die "can t exec date: $!";
  
} else {
   # fork returned 0 nor undef
   # so this branch is parent
   print "Printed by parent process
";
   $ret = waitpid($pid, 0);
   print "Completed process id: $ret
";

}

1;

Printed by parent process
Printed by child process
Tue Sep 17 15:41:08 CDT 2013
Completed process id: 17777

#!/usr/bin/perl

local $SIG{CHLD} = "IGNORE";
 
if(!defined($pid = fork())) {
   # fork returned undef, so unsuccessful
   die "Cannot fork a child: $!";
} elsif ($pid == 0) {
   print "Printed by child process
";
   exec("date") || die "can t exec date: $!";
  
} else {
   # fork returned 0 nor undef
   # so this branch is parent
   print "Printed by parent process
";
   $ret = waitpid($pid, 0);
   print "Completed process id: $ret
";

}

1;

Printed by parent process
Printed by child process
Tue Sep 17 15:44:07 CDT 2013
Completed process id: -1

#!/usr/bin/perl

kill( INT , 104, 102);
 
1;

#!/usr/bin/perl

print "Hello, World
";

=head1 Hello, World Example
This example demonstrate very basic syntax of Perl.
=cut

print "Hello, Universe
";

Hello, World
Hello, Universe

#!/usr/bin/perl

print "Hello, World
";

while(<DATA>) {
  print $_;
}

__END__

=head1 Hello, World Example
This example demonstrate very basic syntax of Perl.
print "Hello, Universe
";

Hello, World

=head1 Hello, World Example
This example demonstrate very basic syntax of Perl.
print "Hello, Universe
";

#!/usr/bin/perl

print "Hello, World
";

__END__

=head1 Hello, World Example
This example demonstrate very basic syntax of Perl.
print "Hello, Universe
";

Hello, World

=pod
=head1 Heading Text
=head2 Heading Text
=head3 Heading Text
=head4 Heading Text
=over indentlevel
=item stuff
=back
=begin format
=end format
=for format text...
=encoding type
=cut

=head1 SYNOPSIS
Copyright 2005 [TUTORIALSOPOINT].
=cut

=head2 An Example List

=over 4
=item * This is a bulleted pst.
=item * Here s another item.
=back
=begin html
<p>
Here s some embedded HTML.  In this block I can
include images, apply <span style="color: green">
styles</span>, or do anything else I can do with
HTML.  pod parsers that aren t outputting HTML will
completely ignore it.
</p>

=end html

An Example List
   This is a bulleted pst.
   Here s another item.
Here s some embedded HTML. In this block I can include images, apply 
styles, or do anything else I can do with HTML. pod parsers that aren t 
outputting HTML will completely ignore it.